The present invention relates to a device in which a slider having a sliding contact is slidingly movable on an electrode pattern, and especially to a contact structure in such a device. More specifically, it relates to an improved contact structure for accurately detecting the position of the slider.
FIGS. 1 and 2 show an example of such a device to which the contact structure according to the present invention can be applied. The device shown in fact is a throttle valve sensor which is adapted to detect the opening degree of a throttle valve employed for controlling an intake air to be admitted into an internal combustion engine.
The device includes a power terminal 2 to be connected to a power supply, so that current is supplied through the terminal 2 to an electrode pattern 28 printed on an insulating substrate 26. The electrode pattern 28 is printed with a conductive material and is connected to another electrode pattern 22 which is printed with a material having a suitable resistance. The electrode pattern 22 is connected to a ground terminal 8. There is provided inside of the electrode pattern 22 a further electrode pattern 20 which is printed with a conductive material and connected to a signal terminal 6.
A sliding contact piece 24 is fixed to a slider (not shown) which is rotated around the center of the electrode patterns 22 and 20 in response to opening and closing of the throttle valve (not shown).
In such a throttle valve sensor as described above, output of the signal terminal 6 is varied in response to the opening degree of the throttle valve, and thus the opening degree of the throttle valve is detected according to the output of the signal terminal 6.
According to this type of sensor, accurate detection of the opening degree of the throttle valve requires stable contact between the power terminal 2 and the electrode pattern 28, stable contact pressure to be applied by a sliding contact piece 24 to the electrode patterns 20 and 22, accurate relative arrangement of the slider and the sliding contact piece 24, and stable contact between the electrode pattern 22 and the ground terminal 8 and between the electrode pattern 20 and the signal terminal 6.
FIG. 10 shows an example of a prior art sliding contact piece. The sliding contact piece 204 is composed of a rectangular base plate 206 and a pair of contact segments 200 and 212 extending from a side 202 of the base plate 206 perpendicularly thereto. The sliding contact piece 204 has a mounting hole 208 formed around the center of the base plate 206 and flat springs 210 provided on the side opposite to the side 202.
FIG. 11 shows a sectional view taken along the line XI--XI in FIG. 10, illustrating the sliding contact piece 204 in FIG. 10 fixed onto a slider 224. The slider 224 includes a face 222 on which the base plate 206 of the sliding contact piece 204 is mounted. The face 222 is formed with an edge portion 220 on the left as viewed in FIG. 11, another edge portion 214 on the right and a projection 216 around the center thereof. When the sliding contact piece 204 is attached to the slider 224 with the mounting hole 208 fitted onto the projection 216, the flat springs 210 are brought into abutment against the edge portion 220 to be deflected, and the side portion 202 is forced against the edge portion 214 to be fixed thereby. Thus, the sliding contact piece 204 is positionally restricted in relation to the slider 224 in the right-to-left direction as viewed in FIG. 11. Keeping the assembly in this condition, a snap member 218 is press-fitted onto the projection 216 from the upside, so that the sliding contact piece 204 is fixed in relation to the slider 224 and positionally restricted in relation thereto in the vertical direction. The slider 224 has a face 226 extending from the face 222, and the meeting line therebetween is a start line of deflection of the contact segments 200 and 212. With this arrangement, the sliding contact piece 204 may be positioned in relation to the slider 224 and be brought into contact with a conductor under a predetermined pressure. The above arrangement is disclosed in detail in Japanese Utility Model Laid-Open Publication No. 59-39905.
Such an arrangement, however, still suffers from the following problems. First of all, the sliding contact piece 204 must be mounted onto the slider 224 with the flat springs deflected, causing a difficult mounting operation. Secondly, the side portion 202 of the sliding contact piece 204 bites into the edge portion 214 to cause inaccurate positioning, especially when the sliding contact piece 204 is formed of a thin plate having a thickness of about 0.1 mm. The third problem is that the base plate 206 of the sliding contact piece 204 will not come into tight contact with the mounting face 222 of the slider 224 but generate undulation on the mounting face 222. This problem is conspicuous, especially when it is in an environment subject to substantial change in temperature and heavy vibration such as in an engine room of an automobile.
FIGS. 12 to 14 show a prior art connecting contact for connecting the electrode patterns 28, 22, 20, 18, etc. with the terminals 2, 8, 6, etc. in FIG. 1 and mounting thereof to the substrate.
As shown in FIG. 12, a connecting contact 232 is a substantially cruciform member having an upper end portion 228 for anchoring and a through hole 230 formed substantially at the center of the end portion 228. FIGS. 13 and 14 show mounting of the connecting contact 232 to the substrate 238 in two sections perpendicular to each other. An electrode pattern 240 is printed on the upper surface of the substrate 238, and the substrate 238 and the electrode 240 have a common square hole 236 through which the end portion 228 of the connecting contact 232 is inserted. The connecting contact 232 inserted into the square hole 236 from the underside is joined to the electrode pattern 240 by solder 234. Preferably, the through hole 230 is filled with the solder 234, as shown in FIG. 14. Thus constructed, the connecting contact 232 is fixed to the substrate 238 and electrical contact is assured between the connecting contact 232 and the electrode pattern 240. This is disclosed in Japanese Patent Laid-Open Publication No. 60-211802.
Such a connecting contact structure, however, suffers from the following problems. First, soldering of the connecting contact 232 to the electrode pattern 240 must be performed, preventing the connecting contact 232 from falling down out of the substrate 238, so that soldering operation is troublesome. Secondly, the essential element for preventing the connecting contact 232 from falling out is the solder filling the through hole 230, but as it cannot be assured that the through hole 230 is filled with the solder, this structure lacks reliability.